This steps to do this are simple, but not necessarily obvious. Here’s what to do.

1. Log in to WordPress admin.
2. Click Pages or Posts (or another post type that your theme might support like Testimonials, Team, Services etc).
3. Open the page or post you want to link to the PDF from.
4. Click Add Media -> Upload Files -> Select Files.
5. Find the PDF file on your computer’s hard drive and click Ok to upload it.
6. Here’s the less than obvious part: You need to copy onto the clipboard of your computer the URL that points to where the file ended up on your website hosting.
   On newer versions of WordPress it is labelled File URL and there is a button labelled Copy URL to clipboard that you just click.
   
   On older WordPress versions it was labelled URL, and you would use your mouse to select the complete contents of that field and then press Control-C (PC) or Command-C (Mac) on your keyboard to copy the URL onto your clipboard. 
7. This step isn’t obvious either. Do NOT click the Insert into post button at the bottom right. Instead click the X at the top right.
8. Back in the text editor for that page/post, decide whether you are going to enter text that links to the PDF or have an image that links to the PDF.
9. If you choose a text link:
   1. Type in the text you want to make into a link. It might be: Download a PDF of our Services.
   2. Select all of that text with the mouse.
   3. Jump to step 11.
10. If you choose an image link:
    1. Insert an image into the web page and position it as you usually would.
    2. Click the image once.
    3. Proceed to step 11.
11. Click the link control in the text editor. It looks like an intact link of a chain.
12. Use Control-V (PC) or Command-V (Mac) to paste the URL you saved on your clipboard (in step 6) into the box. (If there is already a link URL in that box, you do want to overwrite it.)
13. Click the nearby blue button that has the same symbol as the Return/Enter key on your keyboard.
14. If you want the PDF to open in a separate window:
    1. Click the pencil icon.
    2. Click the gear icon to get more options.
    3. Tick the box that says Open link in a new tab.
    4. Click the blue Update button.
15. Save the page post using the Publish or Update button.